Corneal endothelial cells activate innate and acquired arm of anti-viral responses after cytomegalovirus infection

Infection of the corneal endothelial cells by human cytomegalovirus (CMV) is an important cause of corneal endotheliitis. CMV endotheliitis is difficult to completely cure and relapses are frequent. This can cause blinding corneal bullous keratopathy. However, the pathogenesis of CMV endotheliitis remains undetermined. To understand the immunopathology of endotheliitis, we examined how corneal endothelial cells prime the anti-viral immunity after CMV infection based on global transcriptional responses. To accomplish this, human corneal endothelial (HCEn) cells were infected with CMV, and the global transcriptional responses were determined by microarray analyses for primary anti-viral responses using network analysis. Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and protein array analyses were used to examine whether anti-viral cytokines were induced, i.e., to determine whether innate immune responses were activated. To examine whether priming of acquired immune response was activated, CMV-infected HCEn cells were co-cultured with allogeneic CD8⁺ T cells from CMV seropositive donors and tested for priming activity for the CD8⁺ effector T cells by measuring interferon-γ secretion. The CMV-induced responses of HCEn cells were characterized by type I interferon and pattern recognition receptor pathways which represent innate immune priming. The global transcriptional activation was specifically associated with antigen presentation with the antimicrobial response functions. Protein array analyses indicated a significant increase in the secretion of anti-viral inflammatory cytokines including CXCL10 as innate immune responses. When HCEn cells were examined to determine whether CMV infection activated anti-viral acquired immunity, CMV-infected HCEn cells directly stimulated the proliferation of CD8⁺ T cells from CMV-seropositive donors, and pp65 viral epitope induced interferon-γ secretion from the CD8⁺ T cells. We conclude that CMV-infected HCEn cells induce innate immune priming along with provisions of acquired immune priming of CD8⁺ effector T cells. This information should help in the development of useful diagnostic procedures and efficacious therapeutic strategy to treat refractory corneal endotheliitis.

Arginine depletion as a mechanism for the immune privilege of corneal allografts

The cornea is an immune privileged tissue. Since arginase has been found to modulate T-cell function by depleting arginine, we investigated the expression of arginase in the cornea and its possible role in immune privilege using a murine transplant model. We found that both the endothelium and epithelium of murine corneas express functional arginase I, capable of down-regulating T-cell proliferation in an in vitro culture system. The administration of the specific arginase inhibitor N-hydroxy-nor-L-Arg to recipient mice resulted in an accelerated rejection of allogeneic C57BL/6 (B6) corneal grafts. In contrast, in vivo blockade of arginase activity had no effect in altering the course of rejection of primary skin grafts that express little, if any, arginase. In addition, the inhibition of arginase did not alter systemic T-cell proliferation. These data show that arginase is functional in the cornea and contributes to the immune privilege of the eye, and that modulation of arginase contributes to graft survival.

Immune ring formation associated with cytomegalovirus endotheliitis

PURPOSE

To describe immune ring (IR) formation as a manifestation of cytomegalovirus (CMV) endotheliitis.

DESIGN

Retrospective observational case series.

METHODS

Review of all consecutive CMV anterior uveitis and endotheliitis patients seen at the Singapore National Eye Centre for the occurrence of an IR. CMV infection was diagnosed by polymerase chain reaction analysis of the aqueous.

RESULTS

None of the 72 eyes with CMV anterior uveitis had an IR formation. Four episodes of IR formation were seen in 3 eyes (14.3%) of 21 cases of CMV-positive endotheliitis. All were unilateral and all 3 patients were human immunodeficiency virus negative middle-aged Chinese males. The IR developed 2 to 7 months after occurrence of the endotheliitis and the aqueous was positive for CMV during 2 of the episodes of IR formation. In 2 eyes, the IR occurred at the completion of a course of systemic ganciclovir when the aqueous was negative for CMV. The immune rings resolved with combination therapy of topical prednisolone acetate 0.12% and ganciclovir. Patient 1 had a recurrence of the IR 4 months after stopping treatment but again resolved following treatment with ganciclovir and topical corticosteroids.

CONCLUSION

Corneal immune rings can occur as a result of CMV infection. Hence CMV infection may have to be considered in such cases.

Effect of Fas -670 A/G gene polymorphism on corneal allograft endothelial rejection

BACKGROUND

Human cornea expresses functional Fas-ligand capable of killing Fas+ activated lymphocytes. Fas expression is partly regulated by -670 A/G polymorphism in the promoter region of Fas gene.

OBJECTIVE

The aim of the present study is to determine the association between Fas-670A/G polymorphism and survival of corneal transplantation.

METHODS

In 276 graft recipients who mainly underwent penetrating keratoplasty because of keratoconus, bullous keratopathy and corneal opacity, Fas -670 A/G polymorphism was determined by allele specific oligonucleotide polymerase chain reaction (ASO-PCR) techniques.

RESULTS

There was no statistically significant relationship between Fas -670 A/G polymorphism and rejection episode (p=0.35). Moreover, the relationship between this polymorphism and rejection episode outcome (transplant recovery vs failure) was not statistically significant (p=0.13).

CONCLUSION

The results of the present study show no significant correlation between corneal graft rejection, rejection recovery and Fas -670A/G gene polymorphism.

Intrakamerale Applikation von Kortikosteroiden zur Therapie der schweren endothelialen Abstoßung nach perforierender Keratoplastik

Immune reaction is the main cause for graft failure following penetrating keratoplasty. Endothelial immune reaction is the most frequent and most dangerous subtype of rejection because destruction of the graft endothelium can lead to graft failure. "Acute" endothelial rejection is treated by administration of topical and systemic steroids. Intracameral application of corticosteroids by means of an anterior chamber flush is an adjunctive measure that can stop the immune reaction immediately. This measure is thus recommended in all intermediate and severe endothelial rejections.

Will Descemet’s stripping with automated endothelial keratoplasty (DSAEK) lower the rates of allograft rejection in corneal transplants for endothelial failure?

BACKGROUND

Allograft corneal rejection occurs in a substantial number of full thickness transplants in spite of the relative immune privilege enjoyed by the cornea. Compared to other layers of the cornea, endothelial rejection has most disastrous consequences on graft survival. In the last few years, a new technique, Descemet's stripping with automated endothelial keratoplasty (DSAEK) is being used of selective transplantation of the endothelium. It involves stripping diseased endothelium (and Descemet's) and replacing it by a small lamella fashioned from a cadaveric donor cornea, which consists of endothelium, Descemet's membrane and a part of posterior stoma.

HYPOTHESIS

We hypothesize that DSAEK might substantially reduce the incidence of allograft immune rejection in corneal transplant done for cases with endothelial failure.

EVALUATION OF THE HYPOTHESIS

In published reports of consisting of more than 300 surgeries and three years experience with DSAEK, no case of graft rejection has been reported. In our opinion, this advantage of DSAEK compared to conventional full thickness keratoplasty could be due to four factors: (a) The transplanted tissue is placed in the anterior chamber and has no exposure to the surface, where the antigen presenting cells (APC) and antibodies are present. (b) Significant reduction in the number of sutures connecting the host and donor tissue may lead to lesser suture related rejection episodes. (c) Absence of direct contact between the host stroma vessels and the transplanted tissue disrupts the immune affecter and effecter arcs. (d) Reduced immunogenicity of the donated tissue due to absence of epithelium.

CONSEQUENCES OF THE HYPOTHESIS

If this hypothesis stands true in subsequent studies, it could lead to substantial reduction in the socioeconomic resources involved in management of graft rejection. Even if this hypotheses fails the test of well controlled studies, this would broaden the current understanding of the ocular immunology and the immune privilege with which the anterior chamber of the eye is normally associated with.

Differences in leukocyte phenotype and interferon-γ expression in stroma and endothelium during corneal graft rejection

Critical to the success of human corneal transplants is prevention of corneal endothelial rejection, yet little is known about the endothelial infiltrate. To examine the endothelium, a method for removal and processing this layer as a flat sheet was used and the infiltrate was compared with stroma and epithelium. LEW or PVG strain rat corneas were transplanted to PVG strain recipients. Clinical changes after transplantation were monitored by slit lamp and animals sacrificed at a range of time points during rejection. Clinically defined rejection, accompanied by an epithelial rejection line and endothelial cell infiltration, occurred between days 10 and 15. There was some infiltration of leukocytes in the stroma of isografts at these time points, but significantly more in allografts (p<0.003 for all subsets). There was no infiltration of isograft endothelium at any time and no infiltration of allograft endothelium on day 10. On day 15, there were similar numbers of all major subsets except B cells in the stroma, while on the endothelium macrophages, MHC class II(+) cells and CD8(+) cells predominated (p<0.001 CD4(+) vs CD8(+) cells). T cells and NK cells predominated in the epithelial rejection line. While TNF-alpha and IFN-gamma-producing cells were numerous in stroma and epithelium, no IFN-gamma-producing cells were found on endothelium. Distinct differences in infiltrative profile within layers of the cornea suggest that the mechanisms of rejection may also differ. The restricted endothelial cell profile and lack of IFN-gamma suggests that the anti-endothelial response may be modulated by the anterior chamber environment.

Translocation of active heparanase to cell surface regulates degradation of extracellular matrix heparan sulfate upon transmigration of mature monocyte-derived dendritic cells

After Ag capture and exposure to danger stimuli, maturing dendritic cells (DCs) migrate to regional lymph nodes, where antigenic peptides are presented to T lymphocytes. To migrate from peripheral tissue such as the epidermis to regional lymph nodes, Ag-bearing epidermal Langerhans cells must move through an extracellular matrix (ECM) of various compositions. The nature of their capacity to transmigrate via ECM is not well understood, although MIP-3beta and CCR7 play critical roles. We were interested in verifying whether heparanase, a heparan sulfate-degrading endo-beta-d-glucuronidase that participates in ECM degradation and remodeling, is expressed and functional in monocyte-derived DCs. Using immunohistochemistry, confocal microscopy, RT-PCR, Western blot analysis, assays for heparanase activity, and Matrigel transmigration, we show that heparanase is expressed in both nuclei and cytoplasm of immature DCs, and that gene expression and synthesis take place mainly in monocytes and early immature DCs. We also found that both nuclear and cytoplasm fractions show heparanase activity, and upon LPS-induced maturation, heparanase translocates to the cell surface and degrades ECM heparan sulfate. Matrigel transmigration assays showed a MIP-3beta-comparable role for heparanase. Because heparan sulfate glycosaminoglycans play a key role in the self-assembly, insolubility, and barrier properties of the ECM, the results of this study suggest that heparanase is a key enzyme in DC transmigration through the ECM.

Function of indoleamine 2,3-dioxygenase in corneal allograft rejection and prolongation of allograft survival by over-expression

Indoleamine 2,3-dioxygenase (IDO) suppresses T cell responses by its action in catabolising tryptophan. It is important in maintenance of immune privilege in the placenta. We investigated the activity of IDO in the cornea, following corneal transplantation and the effect of IDO over-expression in donor corneal endothelium on the survival of corneal allografts. IDO expression was analysed and functional activity was quantified in normal murine cornea and in corneas following transplantation as allografts. Low levels of IDO, at both mRNA and protein levels, was detected in the normal cornea, up-regulated by IFN-gamma and TNF. Expression of IDO in cornea was significantly increased following corneal transplantation. However, inhibition of IDO activity in vivo had no effect on graft survival. Following IDO cDNA transfer, murine corneal endothelial cells expressed functional IDO, which was effective at inhibiting allogeneic T cell proliferation. Over-expression of IDO in donor corneal allografts resulted in prolonged graft survival. While, on one hand, our data indicate that IDO may augment corneal immune privilege, up-regulated IDO activity following cytokine stimulation may serve to inhibit inflammatory cellular responses. While increasing IDO mRNA expression was found in allogeneic corneas at rejection, over-expression in donor cornea was found to significantly extend survival of allografts.

Prolongation of Sheep Corneal Allograft Survival by Transfer of the Gene Encoding Ovine IL-12-p40 but Not IL-4 to Donor Corneal Endothelium

Immunological rejection is the major cause of human corneal allograft failure. We hypothesized that local production of IL-4 or the p40 subunit of IL-12 (p40 IL-12) by the grafted cornea might prolong allograft survival. Replication-deficient adenoviral vectors encoding ovine IL-4 or p40 IL-12 and GFP were generated and used to infect ovine corneas ex vivo. mRNA for each cytokine was detected in infected corneas, and the presence of secreted protein in corneal supernatants was confirmed by bioassay (for IL-4) or immunoprecipitation (for p40 IL-12). Sheep received uninfected or gene-modified orthotopic corneal allografts. Postoperatively, untreated corneas (n = 13) and corneas expressing GFP (n = 6) were rejected at a median of 21 and 20 days, respectively. Corneas expressing IL-4 (n = 6) underwent rejection at 18.5 days (p > 0.05 compared with controls) and histology demonstrated the presence of eosinophils. In contrast, corneas expressing p40 IL-12 (n = 9) showed prolonged allograft survival (median day to rejection = 45 days, p = 0.003). Local intraocular production of p40 IL-12 thus prolonged corneal graft survival significantly, but local production of the prototypic immunomodulatory cytokine IL-4 induced eosinophilia, inflammation, and rejection. These findings have important implications for the development of novel strategies to improve human corneal graft survival.

[Clinical study on the endothelial immune rejection after penetrating keratoplasty]

OBJECTIVE

To study the relationship between the grafts transparency and the endothelial immune rejection at different periods after penetrating keratoplasty (PKP).

METHODS

A following-up was performed on patients received PKP in Shandong Eye Institute and Hospital between January 1994 and December 1998. A total of 648 cases (648 eyes) were involved in this study, including 444 males (444 eyes) and 204 females (204 eyes). The incidence of endothelial immune rejection and grafts opacification at the time point of 0.5, 1, 3, 6, 9, 12, 18, 24, 36 and 48 months postoperatively was collected. We made two curves to study the relationship between transparence of grafts and endothelial rejection. Relationship between the endothelial immune rejection and the types of corneal diseases before the operation was also analyzed.

RESULTS

There was a significant relationship between grafts opacification and the endothelial immune rejection (linear regression and simple correlation, P < 0.01). The rate of rejection decreased after 3 years postoperatively. Inflammatory background was an important factor for the occurrence of endothelial immune rejection and graft opacification.

CONCLUSIONS

After PKP, endothelial immune rejection is the critical factor for affecting the grafts transparency. Long-term follow-up of the patients is important for the maintaining of transparency of grafts and to obtain a successful result of the operation.

Corneal transplantation: the forgotten graft

The most commonly performed transplant is that of the cornea, with 2292 corneal grafts performed in the UK in 2002-03, compared with 1775 renal transplants [1]. In the USA approximately 40 000 transplants are performed every year [2]. However this preponderance is not reflected in the amount of attention given to this transplanted tissue by the scientific community: for example up till now there have been no papers published in the American Journal of Transplantation that have cornea as a key or title word (as determined by a Medline search in December 2003). There are several reasons for this. The first is that corneal grafting is the province of ophthalmologists, who (with notable exceptions) are isolated from the transplant community. The second is that there is a widespread belief that, because of the existence of immune privilege, corneal grafts are not rejected and so there is no need for further research. As we will discuss later, this is incorrect. In this article we will seek to show that study of corneal transplantation is important in its own right, and also that it has lessons for those interested in other forms of allograft.

Soluble Fas ligand and transforming growth factor beta2 in the aqueous humor of patients with endothelial immune reactions after penetrating keratoplasty

BACKGROUND

Excellent long-term prognosis of penetrating corneal grafts has been explained by the immunological privilege of the cornea and the anterior chamber. In animal models the secretion of transforming growth factor beta(2) (TGF-beta(2)) into the anterior chamber and the expression of the Fas ligand on corneal endothelial cells were identified as important for the integrity of the immunological privilege.

OBJECTIVE

To determine the TGF-beta(2) and soluble Fas ligand (sFasL) levels in the aqueous humor of patients after penetrating keratoplasty (PK) who have and who do not have immune reactions.

METHODS

Anterior chamber puncture was performed in 13 patients who had a cataract without PK (group 1), in 31 patients after PK who did not have immune reactions (group 2), and in 12 patients after PK newly diagnosed as having endothelial immune reactions (group 3). Total TGF-beta(2) and sFasL were determined via enzyme-linked immunosorbent assay.

RESULTS

Transforming growth factor beta(2) was detected in all patients, irrespective of the underlying condition; there was no difference in TGF-beta(2) levels between the different groups (P =.89, analysis of variance). None of the patients in group 1, 11 of 31 patients in group 2, and 8 of 12 patients in group 3 had detectable sFasL concentrations (P =.002, chi(2) test). Soluble Fas ligand averaged (mean [SD]) 20.8 (31.1) pg/mL in group 2, and 38.1 (33.2) pg/mL (P<.01, analysis of variance) in group 3.

CONCLUSIONS

It appears that total TGF-beta(2) is maintained at high steady-state levels, while the level of sFasL is up-regulated in patients who underwent PK, particularily in the advent of graft rejection.

Chronic endophthalmitis mimicking an endothelial immune reaction after penetrating keratoplasty

We describe a patient with chronic inflammation after combined penetrating keratoplasty and cataract surgery. This condition has been considered an unusual endothelial immune reaction. Cytopathological examination of the aqueous humor showed abundant neutrophil granulocytes, a few macrophages, and sparse lymphocytes. The predominance of neutrophil granulocytes but no macrophages or lymphocytes, as found in cases of an endothelial immune reaction, was interpreted as evidence of chronic endophthalmitis. Cytopathological evaluation of aqueous humor can be a helpful tool for differentiating between an endothelial immune reaction and chronic endophthalmitis after combined PKP and cataract surgery.

[Histopathology of herpetic corneal endotheliitis - a case report]

BACKGROUND

Clinically, corneal endotheliitis is characterized by endothelial cell edema associated with immune precipitates. It is supposed to be triggered by a humoral or cellular immunologic reaction against antigens of the corneal endothelium. As yet, only few histopathologic studies of this disease have been performed.

PATIENT

A 42-years-old patient developed a complete corneal nebula with neovascularizations due to relapsing herpetic keratitis. He underwent perforating keratoplasty. The inflammatory infiltrate lining Descemet's membrane and the corneal endothelium consisted mostly of CD 45 R0-positive T-lymphocytes with only few neutrophils, macrophages and CD 20-positive B-lymphocytes. We could not demonstrate any viral particles in the removed corneal tissue by either electron microscopy or using antibodies against Herpes simplex type I or II.

CONCLUSIONS

Histologically, herpetic endotheliitis appears to correspond to corneal endotheliitis due to graft rejection. Complete virus particles are not necessarily required in case of long-standing inflammation and corneal neovascularizations.

[Chronic endothelial cell loss of the graft after penetrating keratoplasty: influence of endothelial cell migration from graft to host]

BACKGROUND

Chronic endothelial cell loss of the graft is common after penetrating keratoplasty. Some kind of subclinical immunological reaction that is not visible at the slitlamp has been suspected as main cause for this phenomenon. Furthermore, migration of graft endothelial cells towards the host cornea has been discussed to add to this loss in special cases. In this study, 3 homogenous patient groups with similar risk of immunological reactions were examined. Main difference between these groups was the potential of graft endothelial cells to migrate towards the host cornea.

PATIENTS AND METHODS

Patients with keratoconus without cataract surgery (group I with little migration potential, n = 273), patients with Fuchs endothelial dystrophy without/with cataract surgery (groups IIa/IIb with moderate migration potential, n = 89/n = 165) and patients with bullous keratopathy after cataract surgery (group III with potentially large migration tendency, n = 188) were included in the study. All patients had a first keratoplasty. Patients with glaucoma or further intraocular procedures after keratoplasty were excluded from the study. Clear graft survival and ratio of grafts without immune reactions were estimated according to Kaplan and Meier. Endothelial analysis concerned only patients without immune reactions and with at least 3 postoperative endothelial cell density values of the graft center (76 patients in I, 18 patients in IIa, 41 patients in IIb and 23 patients in III).

RESULTS

Mean relative loss of endothelial cells per year was 14.0 +/- 19.0 % in group I, 17.0 +/- 19.1 % in group IIa, 20.8 +/- 18.2 % in group IIb and 29.4 +/- 17.6 % in group III (ANOVA, p < 0.01). Five years postoperatively in group I 99 %, in group IIa 98 %, in group IIb 93 % and in group III 69 % of the grafts were centrally clear (log rank test, p < 0.001). In the same period in group I 88 %, in group IIa 86 %, in group IIb 83 % and in group III 81 % of the grafts were free of immune reactions (log rank test, p < 0.05). Reasons for irreversible graft failure were immune reactions (0 in group I; 0 in group IIa; 1 in group IIb; 9 in group III, ), surface disorders (1 in group I; 0 in IIa; 1 in group IIb; 3 in group III) and endothelial failure (0 in group I; 1 in group IIa; 5 in group IIb; 6 in group III) (chi square test, p < 0.01).

CONCLUSIONS

In patients with bullous keratopathy endothelial cell loss via migration seems to add significantly to the general chronic loss which is suspected to be immunological. Peripheral migration of endothelial cells, therefore, most probably contributes to limited prognosis of patients with bullous keratopathy in terms of clear graft survival. In consequence, corneal grafts for bullous keratopathy should be as large as immunologically tolerable, and endothelial cell density should be as high as possible in order to counteract this special endothelial loss factor.

[Purification of corneal endothelial antigen and anti-corneal endothelial antibody]

OBJECTIVE

To explore the methods for purifying corneal endothelial antigen (CEN-Ag) and preparing anti-corneal endothelial antibody (aCEN-Ab).

METHODS

Porcine corneal endothelia were obtained with the epithelia serving as control, CEN-Ag and corneal epithelial antigen (CEP-Ag) were isolated and purified by ion-exchange chromatography and affinity chromatography with 2B4.14.1 monoclonal antibody. The rabbits were immunized with the resultant CEN-Ag and CEP-Ag and their sera collected to harvest aCEN-Ab and anti-corneal epithelial antibody (aCEP-Ab) by affinity chromatography.

RESULTS AND CONCLUSION

The relative molecular mass of CEN-Ag and CEP-Ag were 43 000 and 53 000 respectively as determined by SDS-PAGE, with their immunoglobulins being IgG2 and IgG3.

Immune cells in the anterior chamber of patients with immune reactions after penetrating keratoplasty

PURPOSE

Lymphocytes, monocytes, and macrophages are the predominating immune cells in graft rejection after keratoplasty in animal models. This study focuses on the isolation of immune cells from the anterior chamber of patients with slight, moderate, and severe endothelial immune reactions after penetrating keratoplasty.

METHODS

Anterior chamber puncture was performed in five patients with cataract without inflammation and without penetrating keratoplasty (C1), in three patients undergoing penetrating keratoplasty without immune reactions (C2), in four patients undergoing penetrating keratoplasty after complete resolution of endothelial immune reactions (C3), in seven patients undergoing penetrating keratoplasty with slight endothelial immune reactions (IMI), in 10 patients undergoing penetrating keratoplasty with moderate endothelial immune reactions (IM2), and in eight patients undergoing penetrating keratoplasty with severe endothelial immune reactions (IM3). In each patient, approximately 0.1 mL of aqueous humor was examined. Cells in suspension were directly centrifuged on glass slides using a Cytospin centrifuge, stained, and evaluated under the light microscope.

RESULTS

Groups C1, C2, and C3 did not contain cells. Immune cells were identified in three of seven patients in IM1, in eight of 10 patients in IM2, and in eight of eight patients in IM3. Predominating cells were macrophages and monocytes followed by lymphocytes. Regarding all patients in IMI, IM2, and IM3, a statistically significant correlation between detected cells and patient age, period between penetrating keratoplasty and anterior chamber puncture, or period between first symptoms and anterior chamber puncture could not be revealed. Granulocytes were found statistically significantly less often in patients with high-risk indications, in patients with a history of immune reactions and under immunosuppression. Lymphocytes were found statistically significantly less often in patients with a history of immune reactions.

CONCLUSIONS

The probability to isolate immune cells from the anterior chamber of patients undergoing penetrating keratoplasty correlates with the severity of the endothelial immune reactions. This study is a first step to evaluate how detailed immunologic findings from animal keratoplasty models fit to clinical reality in patients undergoing keratoplasty. In the next step, cells found in the aqueous humor of patients with endothelial immune reactions should be further characterized directly (determination of molecules on the surface of the cells) or indirectly (determination of cytokine levels in the aqueous humor).

[Immunological graft reactions after penetrating keratoplasty - A prospective randomized trial comparing corneal excimer laser and motor trephination]

BACKGROUND AND PURPOSE

Nonmechanical trephination has been established as an advantageous procedure in penetrating keratoplasty (PK) for avascular corneal diseases and has been performed successfully in more than 1000 eyes at our institution. The purpose of this study was to compare incidence, type and reversibility of immunological graft reactions after mechanical and nonmechanical trephination for PK.

PATIENTS AND METHODS

As part of a prospective randomized clinical trial 179 eyes of 76 females and 103 males were included, that had primary central PK without previous intraocular surgery between 10/1992 and 12/1997 for Fuchs' dystrophy (diameter 7.5 mm, n=73) or keratoconus (8.0 mm, n=106). The recipient and donor trephinations were performed from the epithelial side using either a motor trephine (Microkeratron, Geuder, n=91) or an 193-nm excimer laser (MEL60, Aesculap-Meditec, 1.5 x 1.5 mm spot mode, 16 - 24 mJ/pulse, repetition rate 25/s) along round metal masks with 8 "orientation teeth/notches" (n=88). As a routine, donor oversize was 0.1 mm. 128 patients (72 %) had PK only, 51 patients had simultaneous cataract extraction and PC-IOL implantation (triple procedure). Wound closure was achieved using a 16-bite double running diagonal suture by one surgeon (G.O.H.N.). In 53 % of procedures short-term-preserved donor tissue, in 47 % organ-cultured tissue was used. The mean patient/donor age was 51 +/- 17/57 +/- 19 years with nonmechanical trephination and 50 +/- 19/58 +/- 20 years with mechanical trephination. Incidence, type and reversibility of endothelial immunologic graft reactions were recorded continuously by clinical follow-up in an outpatient service with cornea specialization (after 6 weeks, then every 3 months until after suture removal, then every half year).

RESULTS

During a mean follow-up of 40 +/- 15 months, 7.3 % of eyes developed an immunological endothelial graft reaction. Acute diffuse (5.6 %) were more frequent than chronic focal reactions (1.7 %). Only 1.7 % of grafts became irreversibly cloudy. More than 80 % of all graft reactions occurred later than one year (on average 23 +/- 13 months) after PK. Neither incidence (p=0.82, Chi square test) nor cumulative 3-year-rate of immunological graft reactions (p=0.91, LogRank test) differed significantly comparing nonmechanical (6.8 % or 7.3 %) and mechanical (7.7 % or 5.6 %) trephination. In eyes with keratoconus (6.6 %, 16 +/- 8 months) graft reactions did not occur more frequently (p=0.68) but earlier (p=0.02) than in eyes with Fuchs' dystrophy (8.2 %, 31 +/- 11 months). Donor age, post-mortem-time and preservation period did not significantly affect the rate of graft reactions in our study setting.

CONCLUSIONS

Besides well-established optical advantages, nonmechanical trephination using the excimer laser seems to have no immunologic drawbacks in contrast to conventional mechanical trephination. Donor parameters appear to have no major impact on the incidence of graft reactions after non-high-risk PK. Rather, an adequate postoperative therapy with topical steroids, an informed patients' compliance, a consequent long-term follow-up in a clinical out-patient service with corneal specialization and a good education of and cooperation with the referring ophthalmologists are of utmost importance for the clear corneal graft in the long run.

Isolation and characterization of a mouse monoclonal antibody against human corneal endothelial cells

In vitro cultivation of human corneal endothelial cells (HCEC) is associated with loss of typical cobblestone-like appearance during successive passages. Thus far morphology was the sole criterion for the cell's endothelial nature. Mouse monoclonal antibodies (mabs) to human corneal endothelial cells were raised using standard immunization and hybridoma isolation procedures. The specificity of mabs for human corneal endothelial cells was tested in comparison to other endothelial cell types, to fibroblasts, corneal keratocytes and to human retinal pigmented epithelial cells. In addition immunofluorescence or immunoperoxidase staining was performed with frozen tissue sections of human corneas and with various other human tissues. The mab 9.3.E reacts with cultured human corneal endothelial cells, but not with cultured human fibroblasts and human keratocytes. In frozen sections selective positivity of corneal endothelium in contrast to negativity of the other corneal cell types was confirmed. In investigated extraocular tissues positivity was observed in smooth muscle cells including related cells (i.e. Ito and mesangial cells) and in Schwann's cells and adipocytes, but apparently not in vascular endothelial cells. The mab is human-specific and binds to a protein with a molecular weight of 130 kDa mainly accumulating along cell membranes. A mouse monoclonal antibody against human corneal endothelial cells was established in vitro and was shown to be capable of differentiating corneal endothelial cells from other corneal cell types, especially from corneal keratocytes. It is, however, not cornea-specific, but also reacts with certain extraocular cell types.

Immune privilege and immunogenicity reside among different layers of the mouse cornea

PURPOSE

To determine the extent to which each layer of the mouse cornea displays alloimmunogenicity or immune privilege.

METHODS

Intact corneas or individual or combined layers of corneas from normal or cauterized eyes of BALB/c, C57BL/6, and CD95L-deficient B6-gld mice were grafted beneath the kidney capsule of normal BALB/c, B10.D2, BALB.B mice or of BALB/c mice presensitized to donor antigens. Graft fate was assessed clinically and histologically and acquisition of donor-specific delayed hypersensitivity (DH) was assessed at selected intervals after grafting.

RESULTS

Full-thickness allogeneic corneas induced vigorous DH and were rejected acutely. Similar results were obtained with allografts of corneal epithelium alone (if supported by syngeneic viable stroma), allografts of epithelium from cauterized corneas (containing Langerhans' cells), and stromal allografts deprived of endothelium. Grafts comprised of stroma plus endothelium (without epithelium) were not rejected, nor did they induce DH unless the graft had no CD95L expression. If stroma-endothelium grafts had no CD95L expression, DH directed against major histocompatibility complex (MHC), but not minor histocompatibility, alloantigens was induced. Moreover, CD95L expressed on stroma-endothelium grafts protected endothelial cells, but not stromal cells, from rejection in presensitized recipients.

CONCLUSIONS

When grafted to a heterotopic site, the alloimmunogenicity of the normal cornea resides within its epithelial and stromal layers, whereas immune privilege arises from the endothelium. In normal mice, CD95L-expressing endothelium can inhibit the stroma from inducing immunity directed at MHC alloantigens, but in presensitized mice the endothelium can protect itself only from immune rejection.

Labeling of cycling corneal endothelial cells during healing with a monoclonal antibody to the Ki67 antigen (MIB-1)

PURPOSE

To assess the efficacy of labeling actively cycling corneal endothelial cells by using a monoclonal antibody to the Ki67 antigen (MIB-1) and to determine what changes in f-actin and ZO-1 organization are associated with entry into the cell cycle during wound healing under different culture conditions.

METHODS

Three corneal buttons (6 mm diameter) were punched from each cornea of 15 cats. After a mechanical scrape injury (2 mm diameter) was made, buttons were cultured for 24, 48, or 72 h in serum-free media (SFM), SFM plus 10% fetal calf serum, or SFM plus basic fibroblast growth factor (bFGF). Buttons were single and double labeled by using phalloidin, anti-ZO-1, and MIB-1. Counts of Ki67-positive cells were used to determine the number of actively cycling endothelial cells.

RESULTS

After culture in SFM, wounds healed by cell spreading with maintenance of normal apical f-actin and ZO-1 organization; Ki67-positive cells were detected near the leading edge in some areas. A significant increase in the number of cycling cells was measured after 48 h of culture in bFGF as compared with SFM (p<0.05); serum increased the number of cycling cells more than both SFM and bFGF (p<0.05). In all cases, positive MIB-1 staining was not observed until 48 h after injury, was limited to cells actively spreading over the wound area, and was diminished after wound closure (72 h). Double labeling demonstrated that endothelial cells exhibited a fibroblastic phenotype in some central areas of cell proliferation after culture in serum or bFGF, but, in general, apical cell border-associated f-actin and ZO-1 organization was partially maintained in most Ki67-positive cells.

CONCLUSION

The data suggest that spreading corneal endothelial cells are capable of proliferating and can respond to growth factors, but that dedifferentiation or fibroblastic transformation is not required before entry into the cell cycle. Overall, the MIB-1 antibody appears to be ideally suited to the study of corneal endothelial proliferation during wound healing.

An improved method for examining the corneal endothelium during graft rejection in the rat

An improved method of removing rat corneal endothelial sheets for study of endothelial pathology is described. The method was validated by examining morphological changes and changes in expression of major histocompatibility complex (MHC) and intercellular adhesion molecule (ICAM)-1 on endothelium undergoing immunological rejection. PVG strain rats received LEW strain corneal transplants or corneal isografts. Just prior to and during graft rejection, animals were killed, together with a group of untreated animals. The corneal stroma was injected with dispase or PBS, the cornea was carefully removed, fixed in acetone and the endothelium was gently peeled off and flattened on to a glass slide. Morphological changes, together with MHC class I, class II and ICAM-1 expression were visualised by immuno-histochemical staining and quantified by image analysis. Near complete endothelial sheets were obtained by this method. Because of the thin cell layer, there was minimal background staining, permitting rejection-associated changes to be clearly seen. MHC class I expression on normal endothelium was low and not significantly increased on endothelial cells of allografts at the time of rejection compared with controls (P = 0.1). MHC class II and ICAM-1 were induced de novo, expression being significantly higher on allografts than on isografts (P = 0.004 for MHC class II and P = 0.01 for ICAM-1). MHC class I and II and ICAM-1 were expressed on many infiltrating cells. Thus, this preparation method permits clear identification of the distribution and morphology of infiltrating cells and other mediators of the immune response in the entire donor endothelium. It confirms that MHC class I expression is low during rejection, while MHC class II and ICAM-I are induced de novo and strongly expressed.

[Effect of E. coli endotoxin on auto-/paracrine function and endothelial cell loss of donor corneas in organ culture]

Corneal cells are known to participate in the regulation of local inflammatory processes by secretion of cytokines. As the corneal endothelium may be exposed to endotoxin in organ culture and endotoxin is known to trigger inflammatory reactions, we investigated the effect of endotoxin from E. coli on organ cultured donor corneae with respect to autocrine and paracrine functions and the endothelial viability and density. 6 pairs of donor corneae were transferred to organ culture. Medium samples were taken prospectively from day 0 to day 20. On day 10 the medium was changed and one of each pair was incubated with 50 micrograms/ml of endotoxin while the other was immersed in standard organ culture medium. The samples were screened for IL-1, -2, -4, -5, -6, -8, -10, TNF alpha and GM-CSF by ELISA. In addition endothelial cell counts were performed at day 0, after 10 and after 20 days of organ culture, using the fixed frame technique. All endotoxin-incubated organ culture media showed significantly increased IL-6 and -8 levels compared to the fellow cornea and to pre-exposure levels (P < or = 0.004). In the endotoxin-treated corneae a significantly higher endothelial cell loss occurred (P = 0.007) and signs of degeneration were observed. None of the other cytokines (IL-1 alpha, IL-2, IL-4, IL-5, IL-10, GM-CSF and TNF alpha) were detected during either the first (1 to 10-day) or the second (11 to 20-day) phase of incubation. A correlation seems to exist between an increase in IL-6 and -8 induced by endotoxin, and endothelial cell loss in organ culture.

[Immunologic transplant reactions after non-mechanical corneal trepanation with the excimer laser]

BACKGROUND

Nonmechanical trephination has been established as the standard procedure in penetrating keratoplasty (PK) for avascular corneal diseases at our institution. The purpose of this study was to analyze the incidence and reversibility of immunologic graft reactions after nonmechanical trephination and to detect potentially causative factors.

PATIENTS AND METHODS

Out of a total series of 400 nonmechanical PKs, 286 consecutive procedures with sufficient follow-up performed between 07/1989 and 09/1997 were included in the study (104 x keratoconus, 78 x Fuchs' dystrophies, 31 x bullous keratopathies, 28 x ulcers, 25 x avascular scars, 12 x stromal dystrophies, 4 x buphthalmos, 4 x others; 202 x PK only, 84 x combined procedures; 276 first PK). The age of the 138 females and 148 males at the time of surgery ranged from 16 to 89 (mean 55 +/- 19) years. The recipient and donor trephinations were performed from the epithelial side using an 193-mm excimer laser (MEL50 or MEL60, Aesculap-Meditec, 1.5 x 1.5 mm spot mode, 16-24 mJ/pulse, repetition rate 30 or 25/s; metal masks). The shape of the recipient trephination was either circular with four or eight "orientation teeth" (n = 251; 5.0-8.0 mm diameter) or elliptical (n = 35, 6.0 x 7.0 to 7.5 x 8.5 mm diameter). In 62% of procedures fresh or short-term-preserved donor tissue was used, and in 38% of procedures the donor tissue was organ-culture-preserved.

RESULTS

During a mean follow-up of 22 +/- 18 months (maximum 7.7 years), 10 acute diffuse (3 irreversible; 1.0%) and 3 chronic focal endothelial graft reactions occurred (4.5%) not earlier than 4 months and not later than 35 months after PK. Elective procedures (3.5%) resulted in significantly (P = 0.01) less reactions than acute corneal ulcers (14.3%). After 1, 2 and 3 years, the cumulative reaction rates (Kaplan-Meier values) were 1.3%, 6.3% and 13.9% in elective procedures, none of which, however, occurred after 26 elliptical trephinations. With fresh or short-term-preserved donor tissue (4.2%), graft reactions did not happen more frequently but earlier (12 +/- 6 months) than with organ-culture-preserved donor tissue (2.2%, 30 +/- 6 months). In patients with keratoconus (4.9%), reactions occurred more frequently (P = 0.05, LogRank) and earlier than in patients with Fuchs' dystrophy (1.3%).

CONCLUSIONS

In addition to well-established optical advantages, nonmechanical trephination seems to have no immunologic drawbacks.

[Acute and chronic immune reactions after penetrating keratoplasty with normal immune risk]

BACKGROUND

For diagnostic and therapeutic reasons it is important to differentiate between acute and chronic immune reactions. Up to now in the literature as well as in clinical follow-up such a differentiation has been performed only very insufficiently. We analysed retrospectively frequency and type of immune reactions after penetrating keratoplasties with normal immune risk in order to have a data basis for comparison with the corresponding data from our high risk keratoplasties.

PATIENTS AND METHODS

The clinical courses of 646 penetrating keratoplasties with good prognosis performed between 11/1986 and 6/1994 were analysed. The mean patient age was 58 (12-89) years. Only endothelial and stromal immune reactions were recorded.

RESULTS

18% of the grafts suffered from at least one immune reaction during the first 3 postoperative years (Kaplan Meier value). 94% of the grafts without immune reactions remained clear in contrast to 45% of the grafts with immune reactions during this period of time (Kaplan Meier values, Log Rank Test: p < 0.001). 81 immune reactions were observed after 62 keratoplasties. 45 immune reactions (56%) had an acute course (43 endothelial, 2 stromal). 36 (44%) were chronic (31 endothelial, 5 stromal). 93.7% of the grafts without clinical signs of immune reactions, 100.0% of the grafts with only chronic immune reactions and 38.7% of the grafts with only acute immune reactions were clear 3 years postoperatively (Kaplan Meier values). No graft with a combination of acute and chronic immune reactions was clear 3 years postoperatively. 56% of all acute immune reactions occurred during the first postoperative year, 82% during the first 2 and 91% during the first 3 postoperative years. For chronic immune reactions the corresponding values reached 51%, 94% and 100%.

CONCLUSIONS

After penetrating normal-risk keratoplasty acute immune reactions occur more often than chronic immune reactions, but the latter are in fact far more frequent than anticipated. If they are diagnosed in time and treated correctly they do not lead to graft failure in the mean run. Both types occur predominantly during the first 3 postoperative years and only rarely thereafter.

Unexpected expression of thrombospondin 1 by corneal and iris fibroblasts in the pseudoexfoliation syndrome

Pseudoexfoliation (PEX) syndrome is a common, but little known, systemic degenerative condition manifest by the extracellular deposition of a distinctive fibrillar material (PEX material) in various organs. In the eye, PEX material is characteristically found on the surfaces of structures that line the anterior and posterior chambers, and it is associated with cataract and glaucoma. Although PEX material contains several elements normally present in basement membranes, its precise composition remains obscure. Because the glycoprotein thrombospondin 1 (TSP1) can be shown in some basement membranes, we attempted to define its involvement in the composition of PEX material by immunohistochemical analysis of ocular tissues from patients with PEX syndrome. Although we were unable to detect TSP1 in PEX material, we were surprised to find that iris and corneal stromal fibroblasts expressed TSP1. In age-matched normal eyes, iris and corneal fibroblasts did not contain demonstrable TSP1. These observations indicate that TSP1 is not a significant component of PEX material but suggest that, in PEX syndrome, stromal fibroblasts remote from the principal sites of PEX material deposition are altered at the molecular level. The findings add evidence to the theory that PEX syndrome represents a disorder of connective tissue metabolism and intimate that the syndrome involves anomalous production of proteins other than those found in PEX material.

Anterior chamber-associated immune deviation promotes corneal allograft survival

PURPOSE

To determine whether anterior chamber-associated immune deviation (ACAID) promotes corneal allograft survival.

METHODS

CB6F1 mice were grafted with orthotopic corneal transplants from C3H donors (mismatch at the entire major histocompatibility complex plus multiple minor histocompatibility loci) and from NZB donors (mismatch only at multiple minor histocompatibility loci). ACAID was induced by priming in the anterior chamber (AC) with either Ia- spleen cells, Ia+ spleen cells, corneal endothelial cells, or corneal epithelial cells from corneal allograft donors before orthotopic transplantation. The role of ACAID in promoting corneal allograft survival was examined by determining the fate of corneal allografts in splenectomized and eusplenic mice.

RESULTS

Anterior chamber priming produced a modest enhancement of the survival of fully allogeneic C3H corneal allografts. By contrast, AC priming with Ia- NZB spleen cells or NZB corneal endothelial cells results in the permanent acceptance of NZB corneal grafts in 60% and 90% of the CB6F1 hosts, respectively. Abolition of ACAID by splenectomy resulted in a sharp increase in the incidence of graft rejection in donor-host combinations involving multiple minor histocompatibility disparity.

CONCLUSIONS

Anterior chamber priming with alloantigens promotes corneal allograft survival in nonimmune and preimmune hosts. Disruption of the camero-splenic axis prevents the induction of ACAID and greatly increases the risk for corneal allograft rejection.

[Assay of anti-corneal endothelial antibody after penetrating keratoplasty]

OBJECTIVE

To study the effective materials in the immune response and the humoral immunity in graft rejective reaction in the host after penetrating keratoplasty (PKP).

METHODS

PK was performed on 2 groups of monkeys with a 5.5 mm button in a 5.0 mm bed. The heterogroup (human to monkey) had 4 monkeys, and homo-group (monkey to monkey) also 4. Nelken's method was modified. Two kinds of antigens, corneal endothelial and stromal antigens, had been made the first time. Enzyme linked immunosorbent assay (ELISA) was used to detect the anti-corneal endothelial antibody (ACEAb) in the serum and aqueous humor of the host.

RESULTS

After PKP, the anti-corneal stromal antibody did not increase obviously, while the increase of ACEAb was distinct.

CONCLUSION

Humoral immune response can occur in the host after PK, and the effective material is ACEAb.

Isolation and characterization of a unique natural killer cell inhibitory factor present in the anterior chamber of the eye

The eye is a classic example of an immunologically privileged organ. Immune privilege in the anterior chamber is a multifaceted phenomenon that may have evolved to protect delicate ocular tissues from immune-mediated damage. The anterior chamber of the eye is lined with corneal endothelial cells, which are terminally differentiated cells that are incapable of regeneration. Since corneal endothelial cells are crucial for maintaining corneal clarity, damage to these cells leads to impairment of vision and, in some cases, blindness. The absence of constitutive expression of MHC class I molecules on corneal endothelial cells makes them potential targets for NK cell-mediated cytolysis. The aqueous humor (AH) that fills the anterior chamber of the eye and bathes the corneal endothelial surface contains numerous immunomodulatory molecules, such as TGF-beta, which may protect the corneal endothelium from NK cell-mediated damage. Functionally significant levels of TGF-beta are present in AH. In this study, we demonstrate that AH inhibits NK cell-mediated cytotoxicity in vitro, but does not affect cytotoxic T lymphocyte-mediated lysis. The inhibitory effect was immediate and occurred without preincubation of NK cells with aqueous humor. The inhibitory factor could not be neutralized by Abs to TGF-beta, but was abrogated by treating AH with proteases. Inhibition was not simply due to lysis of NK cells, since AH did not alter NK cell viability. Initial purification using gel filtration chromatography showed that the activity was restricted to a single elution peak. Analysis of the active fractions by gel electrophoresis indicated that the inhibitory factor was a single protein of approximately 10 kilodaltons. The NK inhibitory factor might be an important modulator for protecting the corneal endothelium from unbridled NK cell-mediated injury and, thus, might be instrumental in preserving vision.

Comparative analysis of the ability of leucocytes, endothelial cells and platelets to degrade the subendothelial basement membrane: evidence for cytokine dependence and detection of a novel sulfatase

The subendothelial basement membrane (BM) is regarded as an important barrier to the entry of leucocytes into inflammatory sites. This study compares the ability of leucocytes, platelets and endothelial cells (EC) to degrade a [35SO4]-labelled subendothelial extracellular matrix (ECM) and assesses the effect of PMA and various pro-inflammatory cytokines on this degradative activity. The different products of degradation, identified by fast protein liquid chromatography (FPLC) gel filtration chromatography, were indicative of protease, endoglycosidase (heparanase) and exoglycosidase and/or sulfatase activity. In terms of ECM degradation, EC and platelets were the most active, with PMA stimulation further enhancing the degradative activity of these two cell types. Platelets exhibited predominantly heparanase activity whereas the EC degradation products suggested a range of enzymic activities, namely proteases, heparanases and sulfatases. Interestingly, EC in suspension expressed these three enzymic activities whereas confluent EC monolayers only exhibited sulfatase activity, suggesting that the former situation might represent an angiogenic response. In the case of leucocytes, neutrophils and lymphocytes degraded the ECM to a much greater extent than monocytes. Each cell type also differed in the predominant enzymic activities it expressed, for example, heparanase activity by lymphocytes, protease activity by neutrophils and sulfatase activity by monocytes. Furthermore, PMA stimulation was shown to have differential effects on these enzymic activities. Some pro-inflammatory cytokines were found to be cell-type specific in their effects on ECM degradation. Thus, IL-1 + TNF enhanced neutrophil and EC degradation of the ECM but inhibited lymphocyte ECM degradation. In contrast, the chemokine IL-8 enhanced ECM degradation by neutrophils, lymphocytes and EC. Of particular interest was the unique sulfatase activity expressed by EC and monocytes which was induced in EC by TNF + IL-1 and IL-8, whereas in monocytes the sulfatase activity was exclusively induced by the chemokine monocyte chemotactic and activating factor (MCAF). Collectively, the results of this study show that leucocytes differ markedly in the enzymes they express to degrade the BM during extravasation and that PMA and cytokines are cell-type specific in their induction of hydrolytic enzyme activity. These results also indicate that EC may play an important role, not only in the recruitment of leucocytes, but also via sulfatase activity in the preparation of vascular BM for leucocyte extravasion.

Immunohistochemical analysis of the pathogenesis of posterior polymorphous dystrophy

The pathogenesis of posterior polymorphous dystrophy was analyzed by immunohistologic methods. Sections of corneal buttons from two patients undergoing transplantation owing to posterior polymorphous dystrophy were stained with 2B4.14.1, a monoclonal antibody that reacts with human corneal endothelium, and with a cocktail of antihuman cytokeratin monoclonal antibodies that do not react with normal corneal endothelium. Single-stained sections revealed a variegated, intermittent staining pattern of antibody reactive and nonreactive cells. Double-stained sections revealed some cells that stained with only one of the antibodies and many cells that stained with both antibodies. The presence of cells staining positively for both 2B4.14.1 antigen and cytokeratins supports the hypothesis that the cytokeratin-expressing epithelial-like cells found in corneas with posterior polymorphous dystrophy arise via a metaplastic process in which the phenotype of endothelial cells becomes progressively abnormal.

Fibrin induction of interleukin-8 expression in corneal endothelial cells in vitro

PURPOSE

Classically, acute and chronic inflammations are characterized by fibrin deposition and a dynamic influx of leukocytes. This leukocyte recruitment, and associated activation, is thought to be dependent on the generation of leukocyte chemotactic factors (LCF). Although the functional existence of LCF in ocular tissue has been demonstrated, the identity, source(s), and mechanisms of induction of these LCF are unclear. The authors investigate the hypothesis that in vitro corneal endothelial cells produce LCF in response to fibrin-induced activation. They further hypothesize that in vivo this fibrin-induced expression of LCF contributes to the leukocyte accumulation associated with ocular injury.

METHODS

Bovine corneal endothelial cells (BCEC) were co-cultured for 3 to 72 hours with physiologic concentrations of highly purified fibrin (0.125 to 2.0 mg/ml) polymerized in situ. At harvest, the conditioned medium was separated from the fibrin matrix by centrifugation and characterized for the presence and nature of polymorphonuclear leukocyte chemotactic activity. This fibrin-induced LCF was compared to known LCF, such as interleukin-8 (IL-8), using standard physical, chemical, and immunologic parameters.

RESULTS

Conditioned medium from fibrin-treated BCEC exhibited a dose- and time-dependent induction of LCF activity, as verified by checkerboard analysis. This LCF activity was not immunoprecipitated by a polyclonal antibody to bovine fibrinogen, and it was heat stable (60 degrees C, 90 minutes) and protease labile. Isoelectric focusing and gel filtration analysis revealed a major peak of chemotactic activity at pH 8.5 to 9.0 and a molecular weight of 10 kd, respectively. Radioimmunoassay of conditioned medium from fibrin-treated BCEC for IL-8 demonstrated an 11-fold increase in IL-8 antigen for fibrin-treated BCEC compared to control BCEC.

CONCLUSION

In vitro, fibrin induces BCEC expression of LCF activity that includes IL-8. In vivo, this fibrin induction of LCF from corneal endothelial cells probably serves to control both leukocyte recruitment and activation within the anterior chamber in general and to corneal endothelium in particular. These studies provide a foundation for understanding the nature, sources, and mechanisms of the LCF generation that contributes to endocular inflammation.

Corneal endothelial cells block T cell proliferation, but not T cell activation or responsiveness to exogenous IL-2

We previously reported that Ia+ monolayers of LEW rat corneal endothelial (CE) cells were unable to stimulate proliferation of MHC compatible T cell lines or IL-2 release from hybridomas, and inhibited [3H]-thymidine incorporation when added to conventional lymphocyte proliferation assays. Our purpose was to further analyze the mechanism of the inhibitory activity of CE cells on T lymphocyte activation. Mitogen-induced proliferative responses of splenocytes were found to be as susceptible to inhibition by CE cells as previously reported for antigen-specific activation of T cell lines. Antigen presenting cell (APC) antigen pulsing experiments showed that CE cells did not inhibit antigen processing. Flow cytometry and microscopic observation of the co-cultures revealed that T cells became activated in the presence of antigen, APC and CE cells, exhibiting morphologic changes of blast cell formation, although they did not divide unless given exogenous IL-2. However, if T cells were preactivated in the absence of CE cells, they were no longer susceptible to inhibition if subsequently transferred into CE cell-conditioned medium or onto CE cells. Evidence for an inhibitory factor in CE cell culture supernatant was revealed by two approaches: 1) addition of conditioned medium from CE cell cultures led to inhibition of lymphocyte proliferation assays, and 2) split-well assays also demonstrated the existence of a cell-free immunosuppressive factor produced by the CE cells. However, the inhibition mediated by supernatant alone was less potent than that by direct T cell contact with CE cells, implying that cell-cell interaction contributed to the inhibition. Indomethacin, a prostaglandin synthetase inhibitor, did not reverse CE cell-mediated inhibition. Neutralizing antibodies to TGF-beta 1 and 2 did not reverse the inhibition by CE cells. In summary, T cells received activation signals from APC in the presence of CE cells, but proliferation was inhibited unless exogenous lymphokine was added.

Leukocyte adhesion molecules in rejected corneal allografts

Leukocyte adhesion molecules are believed to play a key role in the selective recruitment of different leukocyte populations to inflammatory sites. In this study, we investigated the presence and distribution of intercellular adhesion molecule-1 (ICAM-1), E-selectin (endothelial leukocyte adhesion molecule-1) and vascular cell adhesion molecule-1 (VCAM-1) in 12 rejected corneal allografts and compared the presence of these adhesion molecules with the composition of the associated inflammatory infiltrates. ICAM-1 was focally expressed on corneal epithelial cells and its expression was increased on keratocytes, corneal and vascular endothelial cells particularly at the site of dense infiltration with mononuclear leukocytes. E-selectin was present on endothelial cells of vessels in the stroma of rejected corneal allografts which were characterized by dense infiltration with T cells and macrophages. VCAM-1 was predominantly expressed on inflammatory cells of the macrophage/monocyte lineage, but only sporadically on vascular endothelial cells in the stroma of vascularized rejected corneal allografts. Our results suggest that ICAM-1, E-selectin and VCAM-1 may all be involved in the pathogenesis of corneal allograft rejection, particularly in the generation of the inflammatory infiltrates.

[An etiopathological study of Mooren's ulcer]

With the indirect immuno fluorescence technique (IFT), the authors examined sera from 16 patients with Mooren's ulcer for the presence of antibodies against normal rabbit and human corneal epithelial cells, and determined the percentages of peripheral T-lymphocyte subsets in the patients and 20 controls. The results indicated that (1) antibodies against rabbit corneal epithelial cells were positive in 75% of the patients, and antibodies against human corneal epithelial cells were positive in 37.5%, whereas both antibodies were negative in the controls, and (2) the percentage of OKT8+ in patients was significantly lower, and the OKT4+/OKT8+ ratio significantly higher than in the controls. The authors concluded that regulatory imbalance existed in the immune system of the patients, and Mooren's ulcer was an autoimmunologic eye disease.

'Subthreshold stimulation' of allospecific delayed hypersensitivity by corneal allografts

Corneal allografts contain few or no Ia+ Langerhans' cells and consistently fail to elicit allospecific delayed-type hypersensitivity (DTH). The present study examined the hypothesis that the inability of corneal allografts to induce allospecific DTH was the result of active suppression. However, the results indicated that an initial exposure to corneal allografts provided a subthreshold stimulus for the induction of DTH because hosts that received a second pair of corneal grafts 7 days later developed DTH. By contrast, hosts that received all four corneal allografts simultaneously, failed to display DTH to donor alloantigens. Hosts that received a single set of corneal allografts did not display DTH to donor alloantigens, yet their spleen cells were capable of transferring DTH to hosts subsequently stimulated with a single set of corneal grafts. The capacity of Langerhans' cell-free corneal grafts to prime the host so that a second set of corneal grafts stimulated DTH to donor alloantigens was termed 'subthreshold stimulation of DTH'. The ability of sequential sets of corneal grafts to induce DTH was abolished by fixation with 0.2% paraformaldehyde. Surprisingly, the single cell-layered corneal endothelium was found to be the crucial corneal component necessary for the induction of allospecific DTH. This unique spectrum of corneal alloimmunogenicity may contribute to the immunological privilege and high success rate of corneal allografts.

Antigen presentation of herpes simplex virus by corneal epithelium--an in vitro and in vivo study

Ia antigen (class II antigen) is a histocompatibility antigen that foreign peptides associate with, before antigen presentation to T cells and subsequent triggering of the CD4 T cells. Although corneal epithelium is normally Ia negative it may become Ia positive under abnormal circumstances but the functional significance of this is uncertain. In this study the expression of Ia antigen on corneal epithelium of mice during in vivo primary and secondary herpes simplex keratitis and the in vitro accessory function of corneal epithelium in the presentation of herpes simplex virus (HSV) antigen to in vivo HSV primed T cells were evaluated. Whole mount preparations of corneal epithelium were found to express Ia antigen on days 3, 5, and 7 following corneal inoculation with live HSV. The intensity of the Ia expression was greater in non-immune mice on day 7 after corneal inoculation compared with immune mice. A cellular suspension of corneal epithelium induced HSV primed T cells to proliferate in the presence of HSV antigen. Induction of Ia antigen on corneal epithelium during herpes simplex keratitis may functionally expand the population of antigen presenting cells in the cornea and contribute to T cell activation.

UVB irradiation renders corneal allografts tolerogenic for allospecific delayed hypersensitivity responses

Heterotopic corneal allografts treated with ultraviolet (UV) radiation not only failed to elicit allospecific delayed-type hypersensitivity (DTH) responses in mice but rendered the hosts tolerant to subsequent immunization with normally immunogenic corneal allografts. The immunological tolerance induced by UV-treated grafts was cyclophosphamide sensitive and antigen specific. Adoptive transfer studies revealed that the tolerance to donor alloantigens could be transferred with CD4+, CD8- T cells which suppressed alloimmune DTH responses at the afferent but not the efferent limb. The capacity of UV-treated corneal allografts to induce allospecific tolerance was related to UV irradiation and not simply a result of loss of corneal viability. Formalin-fixed corneal allografts could not produce similar tolerization for DTH responses. Selective debridement of either the corneal epithelium or endothelium revealed that the corneal endothelium was the critical layer necessary for UV-dependent tolerance induction. Furthermore, the initial exposure to UV irradiation must occur through the endothelium and not the epithelium. Thus, the single-cell layered corneal endothelium is the target for the immunomodulatory effects of UV irradiation on corneal allografts.

Expression of SV40 virus large T antigen by recombinant adenoviruses activates proliferation of corneal endothelium in vitro

Infection with the Ad5-SVR4 virus was used to introduce the large T antigen encoding region of the SV40 virus into bovine and human corneal endothelial cells. Expression of large T antigen occurred in 40% of bovine corneal endothelial cells after a 24-h incubation time versus 12% after 8 h of incubation. By 48 h after infection, almost all (92.8%) bovine corneal endothelial cells expressed large T antigen. Bovine and human corneal endothelial cells which expressed large T antigen proliferated and the characteristic morphologic features of corneal endothelium were maintained. This method may enable growth of enough corneal endothelium to perform studies to elucidate the biochemical mechanisms involved in regulating endothelial cell function.

Intercellular adhesion molecule-1 on rat corneal endothelium in experimental uveitis

We studied the expression of the intercellular adhesion molecule-1 (ICAM-1) on the corneal endothelium of the rat in the experimental uveitis induced by interphotoreceptor peptides (R-4) as an immunogen using immunohistochemical methods. ICAM-1, which was not detected in eyes without inflammation, was expressed on the corneal endothelium, vascular endothelium and inflammatory cells, such as monocytes and lymphocytes, in R-4 induced uveitis. The ocular inflammation in the iris, ciliary body and anterior chamber associated with the adherence of inflammatory cells to the corneal endothelium (keratic precipitates) first appeared on the 11th day and were most remarkable on the 14th day and then gradually subsided after 18th day. The expression of ICAM-1 on the corneal endothelium was noticed from the 12th day of immunization to the 16th day and was most prominent on the 14th day but disappeared after the 18th day. The present study proved that ICAM-1 was expressed on the corneal endothelium in anterior uveitis and further indicated that the corneal endothelium modulates the inflammation of the anterior ocular segment by expressing ICAM-1 and forming keratic precipitates.

Isolation and characterization of mouse monoclonal antibodies against a human vascular endothelial cell-specific antigen

A murine hybridoma clone was isolated secreting IgG-antibodies specific for human vascular endothelial cells. The antibody recognized a plasma membrane antigen (designated HECMA-112) of an apparent molecular weight of 112,000. Indirect immunofluorescence with cultured endothelial cells showed a staining pattern clearly distinct from previously described endothelial cell-specific antigens. The antibody bound to untreated as well as ethanol-fixed, confluent human umbilical vein endothelial cells (HUVEC) but not to other human primary cells (corneal endothelial cells, fibroblasts, keratocytes, lymphocytes, thrombocytes, or erythrocytes) or endothelial cells isolated from bovine or porcine aorta. HECMA-112 can be regarded as an additional marker for human vascular endothelial cells in vivo and in vitro.

Heterologous corneal endothelial cell transplantation--human corneal endothelial cell transplantation in Lewis rats

A heterologous corneal endothelial transplantation was attempted using human endothelial cells and a Lewis rat penetrating keratoplasty model. Cultured human endothelial cells were seeded to a Lewis rat cornea, which was denuded of its endothelium. When grafted into the syngeneic Lewis rat, the graft remained clear for at least five days, and then became opaque and edematous because of immune rejection reaction. In contrast, corneas denuded of their endothelium became opaque and edematous immediately after transplantation. These results demonstrate that transplanted endothelial cells have enough antigens to induce rejection reaction even though they have the functional capacity to deturge the cornea.

Corneal autoimmunity in patients with peripheral ulcerative keratitis (PUK) in association with rheumatoid arthritis and Wegener's granulomatosis

Serum antibodies to the cornea were investigated in patients with peripheral ulcerative keratitis (PUK) in isolation or in association with a systemic disease (rheumatoid arthritis or Wegener's granulomatosis). Indirect immunofluorescence on bovine corneal sections demonstrated that antibodies bound to epithelial antigens in two distinct patterns: a lattice-like pattern, probably staining intercellular membrane antigens, and a diffuse pattern covering the entire surface of the epithelium. Both patterns were associated with PUK rather than systemic disease whilst the presence of the lattice pattern was more associated with the onset of the PUK. Immunoblotting of sera to corneal epithelial protein extracts demonstrated that a number of corneal antigens were targeted by antibodies. Two antigens, 54 kDa and 70 kDa, were of particular interest. Antibodies to the 54 kDa antigen, the major corneal-specific antigen, were also detected by enzyme-linked immunosorbent assay (ELISA). Longitudinal studies showed that these antibodies often first occurred after an episode of PUK. Antibodies to the 70 kDa antigen were related to the Wegener's granulomatosis rather than the PUK.

Inhibition of in vitro T cell activation by corneal endothelial cells

Cells and tissues of the anterior uvea and aqueous humor express activities which inhibit immune responses. These activities include soluble factors such as TGF-beta and uncharacterized cell surface interactions. Relatively little is known regarding the immunologic activities of corneal endothelium, despite its potentially important role in contributing to the immune privilege of the anterior chamber and the high success rate of corneal transplantation. In this report, in vitro studies of cultured rat corneal endothelial (CE) cells were done using S-antigen-specific LEW rat T cell lines, or S-antigen-specific T cell hybridomas, to examine the immunologic capabilities of CE cells. Monolayers of LEW rat CE cells were unable to present antigen or a mitogen, Con A, to T cell lines or hybridomas as assessed by the lack of a proliferative response or IL-2 secretion. Furthermore, the CE cells exerted a potent inhibitory effect when added to in vitro proliferation assays of T cell lines stimulated with antigen or Con A. When T cells were preactivated on conventional antigen presenting cells and then transferred to wells containing CE cells, their proliferation was not inhibited. Although CE cells inhibited activation of T cell lines and hybridomas, they did not inhibit the growth of T cell hybridomas or CTLL cells, nor did the CE cells adversely affect the viability of resting T cells cultured on CE monolayers. The inhibitory effect was reversible as preincubation of T cells on CE cells for up to 6 days followed by washes restored T cell responsiveness when assayed on splenocytes. The inability to stimulate proliferative responses was not affected by preincubation of the CE cells with lymphokines which increase MHC antigen expression. The inhibition observed in these assays was not MHC-restricted as CE cells from both LEW and BN rats were equally inhibitory. CE cells from rabbits and cats were also potent inhibitors of T cell activation, suggesting that the mechanism is evolutionarily conserved. The mechanism of inhibition of CE cells is unknown at this time.

Pretransplant and posttransplant antibodies in human corneal transplantation

The purpose of this study was to measure the association between antibody formation and endothelial corneal allograft reactions in 533 consecutive corneal graft recipients. The median follow-up time of these recipients was 732 days. Pretransplant panel-reactive antibodies were not found to be associated with endothelial corneal allograft reactions. Out of 533 recipients, 239 developed posttransplant antibodies during the course of this study. The formation of posttransplant antibodies was frequent in recipients with pretransplant antibodies and in HLA-A,-B-incompatible recipients. Posttransplant antibodies most often appeared within the first six months after transplantation whereas endothelial allograft reactions most often occurred later. Out of 65 recipients who developed PPRA and underwent an allograft reaction, 53 had a PPRA peak prior to, or at about the time of, the allograft reaction. Corneal allograft reaction events diagnosed during the second and third year after surgery were correlated with PPRA formation during the first year after grafting. The 36-month reaction-free survival rate of transplants was estimated at 72% in recipients with PPRA compared with 86% in recipients without PPRA (log rank P value = 0.002). Furthermore, posttransplant antibody formation altered the outcome of corneal allografts in both HLA-A and -B-compatible and -incompatible recipients. These findings suggest that posttransplant antibody development represents a high risk of endothelial corneal allograft reactions.

Endothelial leukocyte adhesion molecule-1 in endotoxin-induced uveitis

Expression of endothelial leukocyte adhesion molecule-1 (ELAM-1) on endothelial cells leads to the attachment of polymorphonuclear leukocytes. The sequential expression of ELAM-1 and major histocompatibility complex (MHC) class II antigen was examined in the eyes of 59 Lewis rats with endotoxin-induced uveitis (EIU) after the injection of Salmonella typhimurium endotoxin. The eyes were enucleated at 2-hr intervals. Hematoxylin and eosin-stained paraffin-embedded sections and immunohistochemically stained cryostat sections were graded by two masked observers. The MHC class II antigen was expressed on cells in the iris and ciliary body 4 hr after injection of endotoxin and on the corneal endothelium, 8 hr postinjection. It was found that ELAM-1 was expressed first on cells of the ciliary body and iris 10 hr after the injection of endotoxin and on the corneal endothelium, 22 hr postinjection. Clinical and histopathologic disease developed 16 hr postinjection. Adherence of polymorphonuclear cells to the corneal endothelium was observed at the time of ELAM-1 expression. In conclusion, expression of ELAM-1 on ocular tissue occurred in EIU and appeared to promote polymorphonuclear cell accumulation in the anterior segment of the eye.

[Human corneal epithelial, stromal and endothelial cells produce interleukin-6]

We have been investigating the production of cytokines in ocular tissues. In this paper, we demonstrated the in vitro production of interleukin-6 (IL-6) by human corneal epithelial, stromal and endothelial cells using enzyme-linked immunosorbent assay (ELISA). In culture supernatant of the stromal cells, the production of immunoreactive IL-6 was induced, depending upon the doses of lipopolysaccharide (LPS) or IL-1 alpha added into the culture. Detectable IL-6 activity in the supernatant of the stromal cells was found 2 hours after addition of IL-1 alpha and the activity increased to a peak level at 48 hours. On the other hand, in the supernatant of the endothelial cells, IL-6 activity was found even in unstimulated-culture, and induced further by LPS stimulation. The molecular weights (MWs) of the IL-6 produced by the epithelial, stromal and endothelial cells were calculated by gel filtration as about 30 kDa. From Western blotting analysis, the MW of IL-6 produced by the stromal cells was also determined to be 30 kDa.

Monoclonal antibody to the corneal endothelium: partial characterization of the antigen and its expression in fetal and adult rabbits

Monoclonal antibodies (mAbs) were developed against corneal endothelial cells (CECs) using cultured bovine CECs as immunogens by the mouse hybridoma technique. One of these mAbs, KP14D10 (IgM type), reacted specifically with CECs in human, bovine and rabbit ocular tissues as judged by immunohistochemical methods. This mAb also reacted with some epithelial cells of human esophageal and gastric glands but not with those of bovine and rabbit origin. The molecular weight of the antigen was determined to be 60,000 Da by the immunoblotting method. This antigenicity was apparently decreased by treatment with hyaluronidase, trypsin, and pronase. In the immunohistochemical study of rabbit fetal corneas, the immunofluorescence appeared specifically in the CECs after the 15th day of gestation and its intensity became stronger as gestation advanced. These results suggest that this antibody would be a valuable tool in the further analysis of corneal development and of divese pathological alterations of CECs.